It is known that the efficient filing of documents by use of microfilm is done using different techniques. One of these techniques is so-called "flow microfilming" which is normally done on continuous lengths of 16 mm film. According to this technique, one advances the unexposed film in synchronism with the document to be microfilmed. The start of the film takes place at the same time the document is fed into the microfilming camera, which continuously exposes the film, which is stopped soon after the document is microfilmed. This technique allows one therefore to microfilm documents of any length--from little cards of size less than A5, up to continuous forms from electronic data processing systems--while assuring film use limited in proportion to the length of the document. Films obtained in such a way are typically placed in the archives as they are obtained, namely in a roll, normally of 30 meters length. If such a film contains microfilmed documents of A4 size, which according to the selected reduction ratio may typically be reduced to fit onto a length of film of one centimeter, in one roll around 3000 "photograms" are contained. To later consult such photograms one must unwind a great portion of the roll. Moreover, no easy system to locate the documents to avoid very long retrieval time is provided.
To make the retrieval easier and faster as well as, under certain aspects, to enable a more flexible filing system a "microfiche" filing system is often preferred. According to this system, documents are microfilmed on a film having a size of around 10.times.15 cm. On such film one gets about 100 photograms from documents sized A4, using a reduction factor of around 28:1. In this case the microfilming system is essentially static: the camera is adapted to position the microfiche in one of a pre-arranged series of standard positions so as to carry out a microfilming of documents one at a time in a fixed exposure position.
This system, as already said, has the advantage of an easier and faster consultation, particularly if the filing of documents is made with reference to a progressive microfiche figure and to a reference figure diagramming the position of the photogram on the microfiche. In this way, an index is provided for each fiche giving X and Y coordinates of each document. One can then simply move the frame of interest beneath the viewing lens. There are also machines which enable the automatic reading of the microfiche, where positioning of the microfiche for reading is performed automatically by making reference to the coordinates of the photogram on the machine.
However, this system has not the flexibility of the "flow microfilming" system described above because it does not allow the microfilming of documents having a length longer than the standard size--e.g., A4--for which the machine was pre-set.
An intermediate solution, which is becoming increasingly popular is the system of microfilming initially with a flow camera, that is, one using continuous reels of film, and afterwards to cut the film into lengths of standard dimension, e.g., 14 cm, and insert them in the channels of jackets, which are transparent envelopes manufactured to contain said film cuttings. Such jackets while having dimensions equal to the microfiche size, cannot be examined in the automatic reading machines above mentioned because, due to use of the flow microfilming system, the position of the photograms does not coincide with the standard coordinate-located reading positions foreseen on the machine, due to the size variation of the microfilmed documents.